GifMinitel is a JavaScript library that can create an animated Gif file. It is targeted to encode Minitel screens, therefore it cannot be used for other types of images.
There exists other Gif encoder written in JavaScript but I needed an encoder which could compute differences between consecutive frames in order to better compress the animation. Available Gif encoders compress all the image every frame, thus generating bigger files.
Another reason was that I wanted to understand how the Gif file works at the lower level.
Have a look at the test.html demonstration